#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>?
int sum(int n)
{
    if (n == 1)
        return 1;
    else
        return n + sum(n - 1);
}

int main() {
    int n, s;
    scanf("%d", &n);
    s = sum(n);
    printf("%d\n", s);
    return 0;
}